You can rip YouTube videos from the command line in Linux and OSX. There could be ways to do this in Windows via Cygwin, but I did not try that.

In Debian Linux, or any other distribution that uses the apt or aptitude package manager, you can get the youtube-dl program by pulling them from the repositories. Run the following command on a terminal window

sudo apt-get update && sudo apt-get install youtube-dl
youtube-dl <youtube vid URL>

It’s also available on macOS. If you use brew, you can get it with this

brew update
brew install youtube-dl

youtube-dl <youtube vid URL>

I think you can also do this in Windows with Cygwin, but I haven’t tried that.